Substrate processing method and apparatus

ABSTRACT

A substrate processing method and apparatus can securely carry out a pre-plating treatment that enables uniform plating in the necessary area of the surface of a substrate. The substrate processing method carries out a cleaning treatment and a catalyst-imparting treatment of a surface of a substrate as pre-plating treatments and then electroless plates a metal film on the catalyst-imparted surface of the substrate. The cleaning treatment is carried out in a wider area of the surface of the substrate than that area to which a catalyst is imparted by the catalyst-imparting treatment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a substrate processing method andapparatus, and more particularly to a substrate processing method andapparatus useful for a pre-plating treatment which may be performedbefore electroless plating for the formation of aninterconnects-protective layer on exposed surfaces of embeddedinterconnects of a conductive material, such as copper, silver or gold,embedded in fine interconnect trenches formed in a surface of asubstrate, such as a semiconductor wafer.

The present invention also relates to a substrate processing unit usefulfor performing processing, such as plating and a pre-plating treatment,of a front surface (lower surface) of a substrate while holding thesubstrate with the front surface facing downward and with a peripheralportion of the front surface sealed. In particular, a substrateprocessing unit is used as a pre-plating treatment unit to perform apre-plating treatment in advance of electroless plating for a formationof an interconnects-protective layer on exposed surfaces of embeddedinterconnects of a conductive material, such as copper, silver or gold,embedded in fine interconnect trenches formed in a surface of asubstrate, such as a semiconductor wafer.

2. Description of the Related Art

As a process for forming interconnects in a semiconductor device, aso-called “damascene process”, which comprises embedding a metal(electric conductor) into trenches for interconnects and contact holes,is coming into practical use. According to this process, aluminum, ormore recently a metal such as silver or copper, is embedded intotrenches for interconnects and contact holes previously formed in aninterlevel dielectric of a semiconductor substrate. Thereafter, extrametal is removed by performing chemical mechanical polishing (CMP) so asto flatten a surface of the substrate.

In a case of interconnects formed by such a process, for example copperinterconnects formed by using copper as an interconnect material,embedded copper interconnects have exposed surfaces after the flatteningprocessing. In order to prevent thermal diffusion of such interconnects(copper), or to prevent oxidation of such interconnects (copper) e.g.during forming thereon an insulating film (oxide film) under anoxidizing atmosphere to produce a semiconductor device having amulti-layer interconnect structure, it is now under study to selectivelycover the exposed surfaces of interconnects with aninterconnects-protective layer (cap material) composed of a Co alloy, aNi alloy or the like so as to prevent thermal diffusion and oxidation ofthe interconnects. Such an interconnects-protective layer of a Co alloy,a Ni alloy or the like can be produced e.g. by performing electrolessplating.

As shown in FIG. 19, for example, fine recesses 4 are formed in aninsulating film 2 of SiO₂ or the like which has been deposited on asurface of a substrate W such as a semiconductor wafer. A barrier layer6 of TaN or the like is formed on the entire surface, and then copperplating, for example, is carried out onto the surface of the substrate Wto fill the fine recesses 4 with copper and deposit copper on theinsulating film 2. Thereafter, CMP (chemical mechanical polishing) iscarried out onto the surface of the substrate W so as to flatten thesurface of the substrate, thereby forming interconnects 8 composed of acopper film in the insulating film 2. Thereafter, aninterconnects-protective layer (cap material) 9 composed of a Co—W—Balloy film is formed e.g. by performing electroless plating selectivelyon the surfaces of interconnects (copper film) 8 to protectinterconnects 8.

A common electroless plating method for the selective formation of theinterconnects-protective layer (cap material) 9 of Co—W—B alloy film onthe surfaces of interconnects 8 generally involves the following processsteps: First, the substrate W such as a semiconductor wafer, which hasundergone the CMP treatment, is immersed in an acid solution e.g. of0.5M H₂SO₄ at the solution temperature of e.g. 25° C. for e.g. oneminute to remove CMP residues, such as copper, remaining on a surface ofan insulating film 2. After cleaning the surface of the substrate W witha cleaning liquid such as ultrapure water, the substrate W is immersedin a mixed solution, e.g. of 0.005 g/L PdCl₂ and 0.2 ml/L HCl, at thesolution temperature of e.g. 25° C. for e.g. one minute to adhere Pd asa catalyst to the surfaces of interconnects 8, thereby activating theexposed surfaces of interconnects 8. Next, after cleaning the surface ofthe substrate W with a cleaning liquid such as ultrapure water, thesubstrate W is immersed in a solution containing e.g. 20 g/L ofNa₃C₆H₅O₇.2H₂O (sodium citrate) at the solution temperature of e.g. 25°C., thereby carrying out neutralization treatment of the surfaces ofinterconnects 8. Thereafter, after washing the surface of the substrateW with ultrapure water, the substrate W is immersed in a Co—W—B platingsolution at the solution temperature of e.g. 80° C. for e.g. 120seconds, thereby carrying out selective electroless plating (electrolessCo—W—B cap plating) onto the activated surfaces of interconnects 8.Thereafter, the surface of the substrate W is cleaned with a cleaningliquid such as ultrapure water. The interconnects-protective layer 9composed of a Co—W—B alloy film is thus formed selectively on thesurfaces of interconnects 8 to protect interconnects 8.

As described above, when forming an interconnects-protective layer (capmaterial) composed of a Co—W—B alloy film by electroless plating, acatalyst-imparting treatment for imparting a catalyst, for example Pd,to the surfaces of interconnects is carried out in advance. Further,removal of CMP residues, e.g. copper, remaining on an insulating film,which treatment is necessary for preventing an interconnects-protectivelayer from being formed on the insulating film, is carried out byusually using an inorganic acid, such as H₂SO₄ or HCl. Accordingly, itis necessary to carry out a neutralization step immediately beforeperforming plating to stabilize the plating process.

In order to securely perform uniform plating in the necessary area ofthe surface of a substrate after performing a pre-plating treatment, itis necessary to securely impart a catalyst only to that area (platingarea) in the catalyst-imparting treatment, and effect a neutralizationtreatment, etc. over the whole area to which a catalyst has beenimparted.

In conventional plating apparatuses, however, a pre-cleaning treatment(chemical cleaning), which is carried out prior to a catalyst-impartingtreatment, a catalyst-imparting treatment and a cleaning treatment(neutralization treatment) after the catalyst-imparting treatment, aregenerally carried out by using devices each having the sameconstruction. Accordingly, the respective areas of a substrate to besubjected to the pre-cleaning (chemical cleaning), to thecatalyst-imparting treatment and to the cleaning (neutralization) afterthe catalyst-imparting treatment are basically the same. With such aconventional apparatus, due to a device error, a variation inpositioning of a substrate when it is held, etc., there is a case wherethat area of the substrate to which a catalyst will be imparted is notentirely pre-cleaned (with a chemical) or a case where the area of thesubstrate to which the catalyst has been imparted is not entirelycleaned (neutralized) later, whereby plating cannot be effected securelyin the necessary area of the surface of the substrate.

The above-described pre-plating treatments are usually carried out byholding a substrate with its front surface facing downward (face down)while sealing a peripheral portion of the front surface with a sealring, and allowing the front surface (lower surface) of the substrate tobe in contact with a pre-plating treatment liquid. In a conventionalsubstrate processing unit, in particular a pre-plating treatment unitfor carrying out such a pretreatment, there is no space between asubstrate and a seal ring, i.e. on the front surface (lower surface)side of the substrate, for taking in and out a robot hand when holdingthe substrate while sealing the peripheral portion with the seal ring orwhen carrying the substrate out after the treatment. It is therefore ausual practice with such a unit to attract and hold on the back surface(upper surface) side of a substrate by a vacuum hand or gripper handwhen transferring the substrate and placing the substrate at apredetermined position on a seal ring or taking the substrate away fromthe seal ring.

However, holding and transferring a substrate by vacuum attraction witha vacuum hand, foe example, generally involves a considerable loss oftime, taking much time to hold the substrate. Further, there is always arisk of fall of the substrate when the substrate held by a vacuum handis transferred at a high speed. It is therefore necessary to use a lowsubstrate transfer speed in order to avoid the risk of fall ofsubstrate, leading to a lowered throughput.

It may be considered to raise the substrate transfer speed by separatelytaking safety measures against the fall of substrate, for example,provision of a mechanical chuck. Such safety measures, however, wouldmake the apparatus complicated. In addition to the foregoing, holding asubstrate by vacuum attraction of the central portion of even the backsurface could cause generation of particles. There is therefore a demandfor a technology that makes it possible to hold a substrate withoutcontact with the other portion of the substrate other than a particularperipheral portion, a so-called edge-cut portion.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above situation inthe related art. It is therefore a first object of the present inventionto provide a substrate processing method and apparatus which cansecurely carry out a pre-plating treatment that enables uniform platingin the necessary area of the surface of a substrate.

It is a second object of the present invention to provide a substrateprocessing unit which can quickly and securely hold a substrate andtransfer the substrate without a risk of fall of the substrate, therebyincreasing the throughput.

In order to achieve the above objects, the present invention provides asubstrate processing method comprising: carrying out a cleaningtreatment and a catalyst-imparting treatment of a surface of a substrateas pre-plating treatments; and then electroless plating a metal film onthe catalyst-imparted surface of the substrate, wherein the cleaningtreatment is carried out in a wider area of the surface of the substratethan that area to which a catalyst is imparted by the catalyst-impartingtreatment.

The above method makes it possible, for example, to fully pre-clean(with a chemical) the whole area of the surface of a substrate to whicha catalyst is to be imparted and fully clean (neutralize) the whole areato which the catalyst has been imparted, whereby plating can then becarried out securely in the necessary area of the surface of thesubstrate.

In a preferred embodiment of the present invention, the cleaningtreatment as a pre-plating treatment comprises pre-cleaning prior to thecatalyst-imparting treatment and cleaning after the catalyst-impartingtreatment. The pre-plating treatments are carried out in the order ofthe pre-cleaning (chemical cleaning), the catalyst-imparting treatmentand the cleaning. (neutralization treatment). Thereafter, electrolessplating is carried out by allowing the surface of the substrate to be incontact with an electroless plating solution.

It is preferred that the area of the surface of the substrate to which acatalyst is imparted by the catalyst-imparting treatment be the same asthat area for which uniform plating is necessary. This prevents acatalyst from being imparted also to an area of the surface of thesubstrate for which plating is unnecessary, thereby preventing theunnecessary area from being plated later.

The present invention also provides a substrate processing apparatuscomprising: a cleaning treatment unit for carrying out a cleaningtreatment of a substrate; and a catalyst-imparting treatment unit forcarrying out a catalyst-imparting treatment of the substrate. respectivetreatment is carried out as a pre-plating treatment by allowing thesurface of the substrate to be in contact with a respective pre-platingtreatment liquid while sealing a peripheral portion of the surface ofthe substrate with a seal ring. The cleaning treatment unit is designedto carry out the cleaning treatment in a wider area of the surface ofthe substrate than that area to which a catalyst is imparted in thecatalyst-imparting treatment unit.

In a preferred embodiment of the present invention, the cleaningtreatment unit and the catalyst-imparting treatment unit have the sameconstruction except that the seal rings have different opening areas.This makes it possible to standardize the respective units.

It is preferred that the area of the surface of the substrate to which acatalyst is imparted in the catalyst-imparting treatment unit be thesame as that area for which uniform plating is necessary.

The present invention also provides a substrate processing unitcomprising: a substrate receiving ring to which a seal ring is mounted;a vertically movable substrate holder having a substrate fixing ring forholding a substrate by nipping a peripheral portion of the substratebetween the substrate fixing ring and the seal ring; and a temporaryretaining section, mounted to the substrate receiving ring andpositioned around the seal ring, for temporarily retaining the substratewhile forming a space between the substrate and the seal ring.

According to the substrate processing unit, a space is formed between asubstrate and the seal ring when temporarily retaining the substrate onthe temporary retaining portion or taking the substrate out of thetemporary retaining portion. A thin drop-in type hand, for example, mayenter (or leave) the space and hold the lower surface side of thesubstrate within the edge-cut width of the substrate. This enablesholding and transfer of the substrate without any risk of fall of thesubstrate.

The substrate processing unit may, for example, be a pre-platingtreatment unit for carrying out a pre-plating treatment of the substrateprior to plating. The pre-plating treatment unit may, for example, be acatalyst-imparting treatment unit for imparting a catalyst to thesurface of the substrate or a cleaning treatment unit for cleaning thesurface of the substrate.

In a preferred embodiment of the present invention, the substratereceiving ring and the substrate fixing ring hold the substrate with itsfront surface facing downward. According to the present invention, evenwith such a face-down type substrate processing unit, the substrate canbe held securely on the front surface (lower surface) side by a hand andtransferred without a risk of fall of the substrate.

In a preferred embodiment of the present invention, the temporaryretaining section is comprised of a plurality of temporary retainingpins which are biased upwardly by an elastic member, and which lowerintegrally with the substrate holder against the elastic force of theelastic member as the substrate holder lowers, and return to theoriginal position as the substrate holder rises.

By temporarily retaining a substrate on the temporary retaining section(temporary retaining pins) and lowering the substrate holder to therebylower the temporary retaining pins, integrally with the substrateholder, against the elastic force of the elastic body, a peripheralportion of the substrate can be nipped between the substrate fixing ringand the seal ring whereby the substrate can be held. Further, by raisingthe substrate holder after completion of processing (treatment) of thesubstrate to thereby allow the temporary retaining pins to return, bythe elastic force of the elastic member, to the original temporaryretaining position, the substrate can be forcibly detached from the sealring by the elastic force and a space for insertion of a hand can beformed between the substrate and the seal ring.

Preferably, the head portion of each temporary retaining pin has aforward tapered surface for guiding the circumferential end surface ofthe substrate and positioning the substrate. Thus, when placing thesubstrate on the temporary retaining pins, positioning of the substratecan be carried out automatically by the tapered surfaces of the headportions of the temporary retaining pins.

The above and other objects, features, and advantages of the presentinvention will be apparent from the following description when taken inconjunction with the accompanying drawings which illustrates preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a layout plan of a substrate processing apparatus (electrolessplating apparatus) according to an embodiment of the present invention;

FIG. 2 is a front view showing a cleaning treatment unit upon transferof a substrate;

FIG. 3 is a front view showing the cleaning treatment unit upon acleaning treatment (chemical cleaning or neutralization treatment);

FIG. 4 is a front view showing the cleaning treatment unit upon purewater cleaning;

FIG. 5 is a cross-sectional view showing a processing head of thecleaning treatment unit upon transfer of a substrate;

FIG. 6 is an enlarged view of the portion A of FIG. 5;

FIG. 7 is a view corresponding to FIG. 6, showing the processing headupon fixing of a substrate;

FIG. 8 is an enlarged sectional view of the main portion of the cleaningtreatment unit, illustrating an opening area of a seal ring;

FIG. 9 is a view corresponding to FIG. 8, illustrating an opening areaof a seal ring of a catalyst-imparting treatment unit;

FIG. 10 is a perspective view of a substrate processing unit(pre-plating treatment unit) according to another embodiment of thepresent invention;

FIG. 11 is a backside view of a lid of FIG. 10;

FIG. 12 is a perspective view showing a fixed frame, a movable frame anda processing head of the substrate processing unit;

FIG. 13 is a front view showing the fixed frame, the movable frame andthe processing head of the substrate processing unit;

FIG. 14 is a cross-sectional view showing the processing head of thesubstrate processing unit upon transfer of a substrate;

FIG. 15 is an enlarged view of the portion A of FIG. 14;

FIG. 16 is a view corresponding to FIG. 15, showing the processing headupon fixing of a substrate;

FIG. 17 is a cross-sectional view showing the processing head of thesubstrate processing unit upon insertion of a hand;

FIG. 18 is an enlarged view of the portion B of FIG. 17; and

FIG. 19 is a cross-sectional diagram illustrating aninterconnects-protective layer formed by electroless plating.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present will now be described withreference to the drawings. The below-described embodiments relate toapplication to a substrate processing apparatus adapted to efficientlyform an interconnects-protective film by electroless plating and also toa substrate processing unit for use in the substrate processingapparatus. The present invention, however, is of course applicable toother substrate processing apparatuses for carrying out electrolessplating and other substrate processing units.

FIG. 1 is a layout plan of a substrate processing apparatus, which isutilized as an electroless plating apparatus, according to an embodimentof the present invention. As shown in FIG. 1, the substrate processingapparatus (electroless plating apparatus) is divided into three areas: aloading/unloading area 10, a cleaning area and a plating area 14. Theelectroless plating apparatus is installed in a clean room, and thepressures in the respective areas are set as follows:

pressure in loading/unloading area 10>pressure in cleaning area12>pressure in plating area 14

Further, the pressure in the loading/unloading area 10 is set to belower than the pressure in the clean room. This prevents air flowingfrom the plating area 14 into the cleaning area 12, prevents air flowingfrom the cleaning area 12 into the loading/unloading area 10, and alsoprevents air flowing from the loading/unloading area 10 into the cleanroom.

In the loading/unloading area 10, there are provided twoloading/unloading units 18 each for placing thereon and housing asubstrate cassette 16 that houses a substrate W having interconnects 8formed in interconnect recesses 4 formed in the surface (see FIG. 19),and a first transfer robot 22 for transferring the substrate W betweenthe substrate cassette 16 and the below-described first temporarystorage stage 24.

In the cleaning area 12, there are provided a first temporary storagestage 24 positioned on the loading/unloading area 10 side, twocleaning/drying treatment units 26 for cleaning and drying the substrateW after plating, positioned on both sides of the first temporary storagestage 24, a first cleaning treatment unit for carrying out a cleaningtreatment (chemical cleaning) as a pre-plating treatment, and a secondtemporary storage stand 30 having a reversing function of reversing thesubstrate W 180 degrees, both positioned on the plating area 14 side.The cleaning/drying treatment unit 26 comprises a roll brushing unit 32and a spin-drying unit 34 which carry out two-step cleaning (scrubcleaning and chemical cleaning) and spin-drying of the substrate W afterplating. Further, a second transfer robot 36 is disposed in the centerof the first temporary storage stage 24, two cleaning/drying treatmentunits 26, the first cleaning treatment unit 28 and the second temporarystorage stage 30 for transfer of the substrate W therebetween.

In the plating area 14, there are provided pairs of catalyst-impartingtreatment units 38 for carrying out as a pre-plating treatment acatalyst-imparting treatment of the surface of the substrate W, secondcleaning treatment units 40 for carrying out as a pre-plating treatmenta cleaning treatment (neutralization treatment) of the catalyst-impartedsurface of the substrate W, and electroless plating units 42 forcarrying out electroless plating of the surface of the substrate W, eachpair being disposed in parallel. Further, a plating solution supplydevice 44 is disposed at one end of the plating area 14. Furthermore, amovable third transfer robot 46 is disposed in the center of the platingarea 14 for transfer of the substrate W between the first cleaningtreatment unit 28, the catalyst-imparting treatment unit 42, the secondcleaning treatment unit 40, the electroless plating unit 42, and thesecond temporary storage stage 30.

A series of electroless plating processing by the electroless platingapparatus will now be described. In the below-described embodiment, asshown in FIG. 19, an interconnects-protective layer (cap material) 9 ofa Co—W—B alloy film is formed selectively on surfaces of interconnects 8to protect the interconnects 8.

First, a substrate W having interconnects 8 formed in a surface (seeFIG. 19) is taken by the first transfer robot 22 out of the substratecassette 16 placed on the loading/unloading unit 18 and housingsubstrates W with their front surfaces facing upward (face up), and thesubstrate W is transferred to and placed on the first temporary storagestage 24. The substrate W on the temporary storage stage 24 istransferred by the second transfer robot 36 to the second temporarystorage stage 30, where the substrate W is reversed 180 degrees so thatits front surface faces downward (face down). The reversed substrate Wis then transferred to the first cleaning treatment unit 28.

In the first cleaning treatment unit 28, the substrate W is held facedown and the following pre-cleaning (chemical cleaning) is carried as apre-plating treatment to the surface of the substrate: An acid solution,such as a 0.5 M H₂SO₄ solution, for example at 25° C., is sprayed towarda surface of the substrate W to remove CMP residues, such as copper,remaining on an insulating film 2 (see FIG. 19). Thereafter, the surfaceof the substrate W is cleaned with a cleaning liquid, such as ultrapurewater.

Next, the substrate W after pre-cleaning is transferred by the thirdtransfer robot 46 to the catalyst-imparting treatment unit 38, where thesubstrate is held face down and a catalyst-imparting treatment of thesurface of the substrate is carried out as a pre-plating treatment.

The catalyst-imparting treatment is carried out, for example, byspraying a solution containing 0.005 g/L of PdCl₂ and 0.2 ml/L of HCl,e.g. at 25° C., toward the substrate W to adhere Pd as a catalyst to thesurfaces of interconnects 8. Thus, a Pd seed as a catalyst seed isformed on the surfaces of interconnects 8, whereby the exposed surfacesof interconnects 8 is activated. Thereafter, the surface of thesubstrate W is cleaned with a cleaning liquid, such as ultrapure water.

The catalyst-imparted substrate W is transferred by the third transferrobot 46 to the second cleaning treatment unit 40, where the substrate Wis held face down and a cleaning treatment (neutralization treatment) ofthe surface of the substrate is carried out as a pre-plating treatment.The cleaning treatment is carried out, for example, by spraying asolution of 20 g/L of Na₃C₆H₅O₇ 2H₂O (sodium citrate) e.g. at 25° C.toward the substrate W to neutralize the surfaces of interconnects 8,and then water-cleaning the surface of the substrate W with e.g.ultrapure water.

The substrate W, which has undergone the pre-electroless platingtreatments, is transferred by the third transfer robot 46 to theelectroless plating unit 42, where the substrate w is held face down andelectroless plating of the surface of the substrate is carried out. Theelectroless plating is carried out, for example, by immersing thesubstrate W in a Co—W—B plating bath at a temperature of about 80° C.e.g. for about 120 seconds to effect selective electroless plating(electroless Co—W—B cap plating) on the activated surfaces ofinterconnects 8, and then cleaning the surface of the substrate W with acleaning liquid, such as ultrapure water. Interconnects-protective layer9 of Co—W—B alloy film (see FIG. 19) is thus selectively formed on thesurfaces of interconnects 8.

Next, the substrate W after the electroless plating is transferred bythe third transfer robot 46 to the second temporary storage stage 30,where the substrate W is reversed so that its front surface faces upward(face up). The reversed substrate W is transferred by the secondtransfer robot 36 to the roll brushing unit 32 of the cleaning/dryingtreatment unit 26, where particles and unnecessary matter adhering tothe surface of the substrate W are removed by a roll-shaped brush.Thereafter, the substrate W is transferred by the second transfer robot36 to the spin-drying unit 34 of the cleaning/drying treatment unit 26,where chemical cleaning and pure water cleaning of the surface of thesubstrate W are carried out, and the cleaned substrate is spin-dried.

The dried substrate W is transferred by the second transfer robot 36onto the first temporary storage stage 24, and the substrate W on thestage 24 is returned by the first transfer robot 22 to the cassette 16placed on the loading/unloading unit 18.

In the case of the embodiment, a Co—W—B alloy film is used as aninterconnects-protective layer 9. Specifically, theinterconnects-protective layer 9 composed of the Co—W—B alloy film isformed by using a plating solution containing cobalt ions, a complexingagent, a pH buffer, a pH adjusting agent, an alkylamine borane as areducing agent, and a compound containing tungsten, and dipping thesurface of the substrate W in the plating solution.

If desired, the plating solution may further contain at least one of astabilizer selected from one or more kinds of heavy metal compounds andsulfur compounds, and surfactant. Further, the plating solution isadjusted within a pH range of preferably 5-14, more preferably 6-10, byusing a pH adjusting agent such as ammonia water or quaternary ammoniumhydroxide. The temperature of the plating solution is generally in therange of 30-90° C., preferably 40-80° C.

The cobalt ions contained in the plating solution may be supplied from acobalt salt, for example, cobalt sulfate, cobalt chloride or cobaltacetate. The amount of the cobalt ions is generally in the range of0.001-1.0 mol/L, preferably 0.01-0.3 mol/L.

Specific examples of the complexing agent may include carboxylic acids,such as acetic acid, and their salts; oxycarboxylic acids, such astartaric acid and citric acid, and their salts; and aminocarboxylicacids, such as glycine, and their salts. These compounds may be usedeither singly or as a mixture of two or more. The total amount of thecomplexing agent is generally 0.001-1.5 mol/L, preferably 0.01-1.0mol/L. Regarding the pH buffer, ammonium sulfate, ammonium chloride andboric acid may be mentioned as specific examples. The pH buffer can beused generally in an amount of 0.01-1.5 mol/L, preferably 0.1-1.0 mol/L.

Regarding the pH adjusting agent, ammonia water and tetramethylammoniumhydroxide (TMAH) may be mentioned as specific examples. By using the pHadjusting agent, the pH of the plating solution is adjusted generallywithin the range of 5-14, preferably 6-10. An alkylamine borane as thereducing agent, dimethylamine borane (DMAB) and diethylamine borane, maybe mentioned. The reducing agent is used generally in an amount of0.01-1.0 mol/L, preferably 0.01-0.5 mol/L.

Examples of the compound containing tungsten may include tangstic acidsand their salts; and heteropoly acids, such as tangstophosphoric acid(e.g. H₃(PW₁₂P₄₀).nH₂O), and their salts. The compound containingtungsten is used generally in an amount of 0.001-1.0 mol/L, preferably0.01-0.1 mol/L.

Besides above described compounds, other known additives may be added tothe plating solution. Examples of usable additive include a bathstabilizer, which may be a heavy metal compound such as a lead compound,a sulfur compound such as a thiocyanate, or a mixture thereof, and asurfactant of an anionic, cationic or nonionic type.

In the case of the embodiment, a Co—W—B alloy is used as aninterconnects-protective layer 9, an interconnects-protective layercomposed of Co—B, Ni—B or Ni—W—B alloy may also be used as aninterconnects-protective layer 9. Further, though the case of usingcopper as an interconnect material has been described, it is alsopossible to use a copper alloy, silver, a silver alloy, gold or a goldalloy etc. other than copper.

A detailed description will now be made of the first cleaning treatmentunit (pre-plating treatment unit) 28, the catalyst-imparting treatmentunit (pre-plating treatment unit) 38 and the second cleaning treatmentunit (pre-plating treatment unit) 40, which are provided in theelectroless plating apparatus shown in FIG. 1 and carry out cleaningtreatments and a catalyst-imparting treatment as pre-plating treatments.The transfer robots 22, 36, 46, which are respectively provided in theareas 10, 12, 14 of the electroless plating apparatus, have a hand thatcan transfer the substrate W face up or face down according to processrequirements. This makes it possible to carry out a series of processsteps for forming an interconnects-protective film by performingelectroless plating sequentially in one apparatus.

The substrate W is reversed only by the temporary storage stage 30.Reversing of the substrate W by rotation of the arm of the transferrobot 22, 36 or 46 is not carried out, thereby avoiding a risk of fallof the substrate W upon transfer of the substrate W by the transferrobot 22, 36 or 46.

The first cleaning treatment unit 28 and the second cleaning treatmentunit 40 have the same construction, though different treatment liquids(chemical liquids) are used. Further, the catalyst-imparting treatmentunit 38 has the same construction as the cleaning treatment units 28, 40except for using a seal ring having a different opening area, asdescribed later.

FIGS. 2 through 8 show the cleaning treatment unit 28 (40). The cleaningtreatment unit 28 (40) employs a two liquid-separation system forpreventing mixing of different liquids, and seals a peripheral portionof the lower surface, i.e. the processing surface (front surface), ofthe substrate W which has been transferred face down and fixes thesubstrate W by pressing on the back surface side.

The cleaning treatment unit 28 (40) includes a fixed frame 52 that ismounted on the upper part of a frame 50, and a movable frame 54 thatmoves up and down relative to the fixed frame 52. A processing head 60,which includes a bottomed cylindrical housing portion 56, openingdownwardly, and a substrate holder 58, is suspended from and supportedby the movable frame 54. In particular, a servomotor 62 for rotating thehead is mounted to the movable frame 54, and the housing portion 56 ofthe processing head 60 is coupled to the lower end of thedownward-extending output shaft (hollow shaft) 64 of the servomotor 62.

As shown in FIG. 5, a vertical shaft 68, which rotates together with theoutput shaft 64 via a spline 66, is inserted in the output shaft 64, andthe substrate holder 58 of the processing head 60 is coupled to thelower end of the vertical shaft 68 via a ball joint 70. The substrateholder 58 is positioned within the housing portion 56. The upper end ofthe vertical shaft 68 is coupled via a bearing and a bracket to a fixedring-elevating cylinder 74 secured to the movable frame 54. Thus, by theactuation of the cylinder 74, the vertical shaft 68 moves verticallyindependent of the output shaft 64.

Linear guides 76, which extend vertically and guide vertical movement ofthe movable frame 54, are mounted to the fixed frame 52, so that by theactuation of a head-elevating cylinder (not shown), the movable frame 54moves vertically by the guide of the linear guides 76.

Substrate insertion windows 56 a for inserting the substrate W into thehousing portion 56 are formed in the circumferential wall of the housingportion 56 of the processing head 60. Further, as shown in FIGS. 6 and7, a seal ring 84 a is provided in the lower portion of the housingportion 56 of the processing head 60, an outer peripheral portion of theseal ring 84 a being sandwiched between a main frame 80 made of e.g.PEEK and a guide frame 82 made of e.g. polyethylene. The seal ring 84 ais to make contact with a peripheral portion of the lower surface of thesubstrate W to seal the peripheral portion.

As shown in FIG. 8, the seal ring 84 a has such an opening area that acleaning treatment can be effected in a cleaning area S₂ which is widerthan a catalyst impartation area S₁ to which a catalyst is imparted bythe catalyst-imparting treatment unit 38. As will be understood, thecleaning area S₂ corresponds to the region surrounded by the seal ring84 a and, as will be described later, the catalyst impartation area S₂corresponds to the region surrounded by the below-described seal ring 84b used in the catalyst-imparting treatment unit 38. The cleaning area S₂is concentrically wider than the catalyst impartation area S₁.

Accordingly, it is possible with the first cleaning treatment unit 28 tofully pre-clean (with a chemical) that area of the surface of thesubstrate to which a catalyst is to be imparted by thecatalyst-imparting treatment unit 38. With the second cleaning treatmentunit 40, it is possible to fully clean (neutralize) the area to which acatalyst has been imparted by the catalyst-imparting treatment unit 38.

On the other hand, a substrate fixing ring 86 is fixed to a peripheralportion of the lower surface of the substrate holder 58. A columnarpusher 90 protrudes downwardly from the lower surface of the substratefixing ring 86 by the elastic force of a spring 88 disposed within thesubstrate fixing ring 86 of the substrate holder 58. Further, a flexiblecylindrical bellows-like plate 92 made of e.g. Teflon (trademark) isdisposed between the upper surface of the substrate holder 58 and theupper wall of the housing portion 56 to hermetically seal the interiorof the housing portion.

When the substrate holder 58 is in a raised position, a substrate W isinserted from the substrate insertion window 56 a into the housingportion 56. The substrate W is then guided by a tapered surface 82 aprovided in the inner circumferential surface of the guide frame 82, andpositioned and placed at a predetermined position on the upper surfaceof the seal ring 84 a. Thereafter, the substrate holder 58 is lowered soas to bring the pusher 90 of the substrate fixing ring 86 into contactwith the upper surface of the substrate W. The substrate holder 58 isfurther lowered so as to press downwardly on the substrate W by theelastic force of the spring 88, thereby forcing the seal ring 84 a tomake pressure contact with a peripheral portion of the front surface(lower surface) of the substrate W to seal the peripheral portion whilenipping the substrate W between the housing portion 56 and the substrateholder 58 to hold the substrate W.

When the head-rotating servomotor 62 is driven while the substrate W isthus held by the substrate holder 58, the output shaft 64 and thevertical shaft 68 inserted in the output shaft 64 rotate together viathe spline 66, whereby the substrate holder 58 rotates together with thehousing portion 56.

As shown in FIGS. 2 through 4, positioned below the processing head 60,there is provided an upward-open treatment tank 100 having a slightlylarger inner diameter than the outer diameter of the processing head 60.In the treatment tank 100 is disposed a plurality of sprays nozzles (notshown) for spraying upwardly a chemical liquid supplied from a chemicalliquid supply source, which nozzles are distributed evenly over theentire cross-section of the treatment tank 100. A discharge pipe (notshown) for discharging out the chemical liquid (waste liquid) isconnected to the bottom of the treatment tank 100.

A pair of leg portions 104, which is mounted to a lid 102, is rotatablysupported on the outer circumferential surface of the treatment tank100. Further, a crank 106 is integrally coupled to each leg portion 106,and the free end of the crank 106 is rotatably coupled to the rod 110 ofa lid-moving cylinder 108. Thus, by the activation of the lid-movingcylinder 108, the lid 102 moves between a treatment position at whichthe lid 102 covers the top opening of the treatment tank 100 and aretreat position beside the treatment tank 100. In the surface (uppersurface) of the lid 102 are provided a large number of pure water spraynozzles 112 for spraying outwardly (upwardly) pure water supplied from apure water supply source.

By lowering the processing head 60 holding the substrate so as to coveror close the top opening of the treatment tank 100 with the processinghead 60 and then spraying a chemical liquid from the spray nozzlesdisposed in the treatment tank 100 toward the substrate W, the chemicalliquid can be sprayed uniformly onto the entire lower surface(processing surface) of the substrate W and the chemical liquid can bedischarged out from the discharge pipe while preventing scattering ofthe chemical liquid to the outside. Further, by raising the processinghead 60 and closing the top opening of the treatment tank 100 with thelid 102, and then spraying pure water from the pure water spray nozzles112 disposed in the upper surface of the lid 102 toward the substrate Wheld in the processing head 60, the chemical treatment of the substrateW and the pure water cleaning after the chemical treatment can becarried out successively, while the pure water can be prevented fromflowing into the treatment tank 100, avoiding mixing of the two liquids.

According to the cleaning treatment unit 28 (40), the substrate W isinserted into the processing head 60 and held therein when theprocessing head 60 is in the raised position, as shown in FIG. 2.Thereafter, as shown in FIG. 3, the processing head 60 is lowered to theposition at which it covers the top opening of the treatment tank 100.While rotating the processing head 60 and thereby rotating the substrateW held in the processing head 60, a chemical liquid is sprayed from thespray nozzles disposed in the treatment tank 100 toward the substrate W,thereby spraying the chemical liquid uniformly onto the entire surfaceof the substrate W. Thereafter, the processing head 60 is raised andstopped at a predetermined position and, as shown in FIG. 4, the lid 102in the retreat position is moved to the position at which it covers thetop opening of the treatment tank 100. Pure water is then sprayed fromthe pure water spray nozzles 112 disposed in the upper surface of thelid 102 toward the rotating substrate W held in the processing head 60.The chemical treatment and the pure water cleaning of the substrate Wcan thus be carried out successively while avoiding mixing of the twoliquids.

The lowermost position of the processing head 60 may be adjusted toadjust the distance between the substrate W held in the processing head60 and the spray nozzles, whereby the region of the substrate W ontowhich the chemical liquid is sprayed from the spray nozzles and thespraying pressure can be adjusted as desired.

An acid solution, for example a H₂SO₄ solution, is used as the chemicalliquid in the case of the first cleaning treatment unit 28, while asodium citrate solution, for example, is used as the chemical liquid inthe case of the second cleaning treatment unit 40. In either case, thetreated surface of the substrate is cleaned with pure water before it issent to the next process step.

FIG. 9 shows the main portion of the catalyst-imparting treatment unit38, representing a distinctive feature from the above-described cleaningtreatment unit 28 (40). In particular, the catalyst-imparting treatmentunit uses as a seal ring 84 b, which is disposed with its outerperipheral portion sandwiched between the main frame 80 and the guideframe 82 and which makes contact with a peripheral portion of the lowersurface of the substrate W to seal the peripheral portion, one havingsuch an opening area that the catalyst impartation area S₁ is narrowerthan the cleaning area S₂, that is cleaned by the cleaning treatmentunit 28 (40), and is the same as that area of the surface of thesubstrate in which uniform plating is to be carried out.

As will be understood, the catalyst impartation area S₁ corresponds tothe region surrounded by the seal ring 84 b and, as described above, thecleaning area S₂ corresponds to the region surrounded by the seal ring84 a. The catalyst impartation area S₁ is concentrically narrower thanthe cleaning area S₂ and identical to the plating area in which uniformplating is to be carried out.

This prevents a catalyst from being imparted also to a portion of thesurface of the substrate for which plating is unnecessary, therebypreventing the unnecessary portion from being plated later. Further, asdescribed previously, the first cleaning treatment unit 28 can fullypre-clean (with a chemical) that area of the surface of the substrate towhich a catalyst is to be imparted by the catalyst-imparting treatmentunit 38, and the second cleaning treatment unit 40 can fully clean(neutralize) the area to which the catalyst has been imparted by thecatalyst-imparting treatment unit 38. Accordingly, plating can becarried out securely in the necessary area of the surface of thesubstrate.

A solution of PdCl₂ and HCl, for example, may be used as a chemicalliquid in the catalyst-imparting treatment unit 38. As with theabove-described cleaning treatment units 28, 40, after imparting acatalyst to the necessary area of the surface of the substrate, thesubstrate is cleaned with pure water and then sent to the next processstep.

As described hereinabove, the present invention makes it possible, incarrying out pre-electroless plating treatments of the surface of asubstrate, to securely pre-clean (with a chemical) the whole area of thesurface of the substrate to which a catalyst is to be imparted and clean(neutralize) the whole area to which the catalyst has been imparted,thereby enabling a later plating to be carried out securely in thenecessary area of the surface of the substrate.

A detailed description will now be made of a substrate processing unitaccording to another embodiment of the present invention, which isusable as the first cleaning treatment unit (pre-plating treatment unit)28, the catalyst-imparting treatment unit (pre-plating treatment unit)38 and the second cleaning treatment unit (pre-plating treatment unit)40 which are provided in the electroless plating apparatus shown in FIG.1 and carry out cleaning treatments and a catalyst-imparting treatmentas pre-plating treatments.

The same substrate processing unit of this embodiment can be used as thefirst cleaning treatment unit 28 disposed in the cleaning area 12, andas the catalyst-imparting treatment unit 38 and the second cleaningtreatment unit 40 both disposed in the plating area 14, though differenttreatment liquids (chemical liquids) are used in these treatment units.FIGS. 10 through 18 show the substrate processing unit (pre-platingtreatment unit) 150 which is used as the respective treatment unit. Thesubstrate processing unit 150 employs a two-liquid separation system forpreventing mixing of different liquids, and seals a peripheral portionof the lower surface, i.e. the processing surface (front surface), ofthe substrate W which has been transferred face down, and fixes thesubstrate W by pressing on the back surface.

The substrate processing unit 150 includes a fixed frame 154 that ismounted on the upper portion of a frame 152, and a movable frame 156that moves up and down relative to the fixed frame 154. A processinghead 162, which includes a bottomed cylindrical housing portion 158opening downwardly, and a substrate holder 160, is suspended from andsupported by the movable frame 156. In particular, a servomotor 164 forrotating the head is mounted to the movable frame 156, and the housingportion 158 of the processing head 162 is coupled to the lower end ofthe downward-extending output shaft (hollow shaft) 166 of the servomotor164.

As shown in FIG. 14, a vertical shaft 170, which rotates together withthe output shaft 166 via a spline 168, is inserted in the output shaft166, and the substrate holder 160 of the processing head 162 is coupledto the lower end of the vertical shaft 170. The substrate holder 160 ispositioned within the housing portion 158. The upper end of the verticalshaft 170 is coupled via a bearing 172 and a bracket 174 to a fixedring-elevating cylinder 176 secured to the movable frame 156. Thus, bythe actuation of the cylinder 176, the vertical shaft 170 movesvertically independent of the output shaft 166.

A hook 180 is mounted to the back surface of the movable frame 156 onthe fixed frame 154 side, extending backward from the movable frame 156through a vertically-extending slit 154 a formed in the fixed frame 154.The hook 180 is coupled to the upper end of the rod of a head-elevatingcylinder 182 that is mounted to the fixed frame 154. Linear guides 184,which extend vertically and guide vertical movement of the movable frame156, are mounted to the fixed frame 154, so that by the actuation of thehead-elevating cylinder 182, the movable frame 156 moves vertically bythe guide of the linear guides 184.

Further, the fixed frame 154 is provided with a stopper 186 for headposition fixing, while the movable frame 156, at a positioncorresponding to the stopper 186, is provided with a bolt 188 for headposition adjustment, respectively. The lowermost position of theprocessing head 162 can be fixed mechanically by allowing the adjustmentbolt 188 to make contact with the stopper 186. Further, the lowermostposition of the processing head 162 can be adjusted by adjusting theposition of the stopper 186. In addition, fine adjustment of thelowermost position of the processing head 162 can be made with theadjustment volt 188.

Substrate insertion windows 158 a for inserting the substrate W into thehousing portion 158 are formed in the circumferential wall of thehousing portion 158 of the processing head 162. As shown in detail inFIGS. 15 and 16, positioned on the upper surface of an inner peripheralportion of a substrate receiving ring 190, a seal ring 192, projectingupwardly in a tapered cross-sectional shape, is fixed in the lowerportion of the housing portion 158 of the processing head 162. The sealring 192 is to make contact with a peripheral portion of the lowersurface (front surface) of the substrate W to seal the peripheralportion. Further, a plurality of temporary retaining pins (four pins areshown) 194 as a temporary retaining section for temporarily retainingthe substrate W are disposed at positions around the outer periphery ofthe seal ring 192 of the substrate receiving ring 190. Each temporaryretaining pin 194 is biased upwardly by a helical compression spring 196which is housed in a recess 190 a formed in the substrate receiving ring190. A stopper strip 198 mounted on the upper surface of the substratereceiving ring 190 engages a step portion 194 a which is formed almostat the middle of the shaft portion of the temporary retaining pin 194,thereby preventing the temporary retaining pin 194 from escaping upward.

The upwardly-projecting head portion of the temporary retaining pin 194has a forward tapered surface 194 b which, when placing the substrate Won the temporary retaining pin 194, contacts the peripheral end surfaceof the substrate W and effects positioning of the substrate W, and aretaining portion 194 c, projecting outwardly in a flange shape, forplacing thereon and retaining a peripheral lower surface of thesubstrate W, the tapered surface 194 b and the retaining portion 194 cbeing continuous. A peripheral portion of the lower surface (frontsurface) of the substrate W may be supported, within the edge-cutregion, by a hand H e.g. of a thin drop-in type, and transferred toabove the temporary retaining pins 194 in the housing portion 158. Whenthe hand H is lowered, the substrate W is guided and positioned by thetapered surface 194 b of the respective pin 194, and placed andtemporarily retained on the retaining portion 194 c. When the substrateW is thus temporarily retained, a space S is formed between thesubstrate W and the substrate receiving ring 190, and the hand H can bedrawn from the space S. The temporary retaining pins 194, inconsideration of corrosion, may be coated e.g. with Teflon (trademark).

On the other hand, a substrate fixing ring 200, having in the outerperipheral lower surface a downward-expanding expanded portion 200 a, ismounted integrally to a peripheral portion of the lower surface of thesubstrate holder 160 at a position corresponding to the seal ring 192.Further, the substrate holder 160 has in the peripheral portion, atpositions corresponding to the temporary retaining pins 194, pressingportions 160 a, projecting downwardly, for pressing down the temporaryretaining pins 194. The positional relationship in the height directionbetween the substrate fixing ring 200, the pressing portion 160 a andthe temporary retaining pin 194 is set as follows.

As the substrate holder 160 lowers, the pressing portion 160 a of thesubstrate holder 160 first comes into contact with the upper surface ofthe head portion of the temporary retaining pin 194. As the substrateholder 160 further lowers, the pressing portion 160 a presses down thetemporary retaining pin 194 against the elastic force of the helicalspring 196. The substrate holder 160 continues to lower even after thelower surface of the substrate W comes into contact with the seal ring192, thereby nipping a peripheral portion of the substrate W between theseal ring 192 and the substrate fixing ring 200 and allowing the sealring 192 to make pressure contact with a peripheral portion of the frontsurface (lower surface) of the substrate to seal the peripheral portion.As the substrate holder 160 further lowers, a slight gap G is formedbetween the substrate W and the retaining portion 194 c of the temporaryretaining pin 194, and the substrate W becomes fixed only by the sealring 192 and the substrate fixing ring 200.

When the substrate holder 160 is raised after treatment of the substrateW, the temporary retaining pin 194 rises by the elastic force of thehelical spring 196, and catches a peripheral portion of the treatedsubstrate W on the retaining portion 194 c and detaches the substrate Wfrom the seal ring 192. The temporary retaining pin 194 further risesalong with the substrate W, and stops rising by engagement of the stepportion 194 a with the stopper strip 198. The substrate W is thusreturned to the temporary retaining position. By thus forcibly detachingthe substrate W from the seal ring 192 by the elastic force of thehelical spring 196, the substrate can be securely detached from the sealring 192 even when the substrate W has adhered to the seal ring 192during treatment. Further, by returning the substrate W to the temporaryretaining position after treatment, it becomes possible to insert thehand H, e.g. of a thin drop-in type, into the space S formed between thesubstrate W in the temporary retaining position and the substratereceiving ring 190, hold the substrate W securely on the hand H, andtransfer the substrate W by the hand H to the next process step.

In operation, when the substrate holder 160 is in a raised position, thehand H, e.g. of a thin drop-in type, holding thereon a peripheralportion of the lower surface (front surface) of the substrate W, isinserted from the substrate insertion window 158 a into the housingportion 158 so as to position the substrate W above the temporaryretaining pins 194. The hand H is then lowered so as to place thesubstrate W at a predetermined position on the retaining portion 194 cby the guide of the tapered surface 194 b. FIGS. 17 and 18 show theprocessing head 162 upon insertion of the hand H. After further loweringthe hand H, the hand H is drawn from the space S between the substrate Wand the substrate receiving ring 190. Thereafter, the substrate holder160 is lowered to fix the substrate W by nipping the peripheral portionbetween the seal ring 192 and the substrate fixing ring 200 in theabove-described manner.

When the head-rotating servomotor 164 is driven while the substrate W isthus held in the processing head 162, the output shaft 166 and thevertical shaft 170 inserted in the output shaft 166 rotate together viathe spline 168, whereby the substrate holder 160 rotates together withthe housing portion 158.

As shown in FIGS. 10 through 11, positioned below the processing head162, there is provided an upward-open treatment tank 202 having aslightly larger inner diameter than the outer diameter of the processinghead 162. In the treatment tank 202 is disposed a plurality of spraysnozzles 204 for spraying upwardly a chemical liquid supplied from achemical liquid supply source, which nozzles are distributed evenly overthe entire cross-section of the treatment tank 202. A discharge pipe(not shown) for discharging out the chemical liquid (waste liquid) isconnected to the bottom of the treatment tank 202.

A pair of leg portions 208, which is mounted to a lid 206, is rotatablesupported on the outer circumferential surface of the treatment tank202. Further, a crank 210 is integrally coupled to each leg portion 208,and the free end of the crank 210 is rotatably coupled to the rod 214 ofa lid-moving cylinder 212. Thus, by the activation of the lid-movingcylinder 212, the lid 206 moves between a treatment position at whichthe lid 206 covers the top opening of the treatment tank 202 and aretreat position beside the treatment tank 202. In the surface (uppersurface) of the lid 206 are provided a large number of pure water spraynozzles 216 for spraying outwardly (upwardly) pure water supplied from apure water supply source.

By lowering the processing head 162 holding the substrate so as to coveror close the top opening of the treatment tank 202 with the processinghead 162, and then spraying a chemical liquid from the spray nozzles 204disposed in the treatment tank 202 toward the substrate W, the chemicalliquid can be sprayed uniformly onto the entire lower surface(processing surface) of the substrate W and the chemical liquid can bedischarged out from the discharge pipe while preventing scattering ofthe chemical liquid to the outside. Further, by raising the processinghead 162 and closing the top opening of the treatment tank 202 with thelid 206, and then spraying pure water from the pure water spray nozzles216 disposed in the upper surface of the lid 206 toward the substrate Wheld in the processing head 162, the chemical treatment of the substrateW and the pure water cleaning after the chemical treatment can becarried out successively, while the pure water can be prevented fromflowing into the treatment tank 202, avoiding mixing of the two liquids.

According to the substrate processing unit 150, the substrate W isinserted into the processing head 162 and held therein when theprocessing head 162 is in the raised position. Thereafter, theprocessing head 162 is lowered to the position at which it covers thetop opening of the treatment tank 202. While rotating the processinghead 162 and thereby rotating the substrate W held in the processinghead 162, a chemical liquid is sprayed from the spray nozzles 204disposed in the treatment tank 202 toward the substrate W, therebyspraying the chemical liquid uniformly onto the entire surface of thesubstrate W. Thereafter, the processing head 162 is raised and stoppedat a predetermined position, and the lid 206 in the retreat position isthen moved to the position at which it covers the top opening of thetreatment tank 202. Pure water is then sprayed from the pure water spraynozzles 216 disposed in the upper surface of the lid. 206 toward therotating substrate W held in the processing head 162. The chemicaltreatment and the pure water cleaning of the substrate W can thus becarried out successively while avoiding mixing of the two liquids.

The lowermost position of the processing head 162 may be adjusted toadjust the distance between the substrate W held in the processing head162 and the spray nozzles 204, whereby the region of the substrate Wonto which the chemical liquid is sprayed from the spray nozzles 204 andthe spraying pressure can be adjusted as desired.

An acid solution, for example a H₂SO₄ solution, is used as the chemicalliquid in the case of using the substrate processing unit 150 as thefirst cleaning treatment unit 28; a solution of PdCl₂ and HCl, forexample, is used as the chemical liquid in the case of using thesubstrate processing unit 150 as the catalyst-imparting treatment unit38; and a sodium citrate solution, for example, is used as the chemicalliquid in the case of using the unit substrate processing 150 as thesecond cleaning treatment unit 40. In any case, the treated substrate iscleaned with pure water before it is sent to the next process step.

According to the substrate processing unit (pre-plating treatment unit)150, when transferring the substrate W into the processing head 162 ofthe substrate processing unit 150, the substrate W is first placed andtemporarily retained on the retaining portion 194 c of the temporaryretaining pin 194. When the substrate W is temporarily retained, a spaceS is formed between the substrate W and the substrate receiving ring190, and a hand H can be drawn from the space S. Thus, it is possible tohold the substrate W on its lower surface side by a hand H e.g. of athin drop-in type, and place and temporarily retain the substrate W onthe retaining portion 194 c of the temporary retaining pin 194 without arisk of fall of the substrate W. Further, by lowering the substrateholder 160, a peripheral portion of the substrate W can be nippedbetween the seal ring 192 and the substrate fixing ring 200 whereby thesubstrate W can be held securely. Further, by raising the substrateholder 160 after treatment, the substrate W can be securely detachedfrom the seal ring 192 by the elastic force of the helical spring 196even when the substrate W has adhered to the seal ring 192, and can bereturned to the temporary retaining position. As with theabove-described thin drop-in type hand H can be inserted into the spaceS, and can securely hold thereon the lower surface (front surface) ofthe substrate W and transfer the substrate W to the next process step.

As described hereinabove, according to the present invention, a space isformed between a substrate and the seal ring when temporarily retainingthe substrate on the temporary retaining portion or taking the substrateout of the temporary retaining portion. A thin drop-in type hand, forexample, can enter (or leave) the space and hold the lower surface ofthe substrate, enabling holding and transfer of the substrate withoutany risk of fall of the substrate. This makes it possible to shorten thetime taken for holding the substrate and, in addition, raise thesubstrate transfer speed, thereby increasing the throughput.

Although certain preferred embodiments of. the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

1. A substrate processing unit that includes: a substrate receiving ringto which a seal ring is mounted; a vertically movable substrate holderhaving a substrate fixing ring movable so as to hold a substrate bynipping a peripheral portion of the substrate between the substratefixing ring and the seal ring to seal the peripheral portion of thesubstrate during processing of the substrate; and a temporary retainingsection, that is mounted to the substrate receiving ring and positionedaround the seal ring to temporarily retaining the substrate thereonwhile forming a space between the substrate and the seal ring; whereinthe substrate receiving ring and the substrate fixing ring hold thesubstrate with its front surface facing downward; wherein the temporaryretaining section is comprised of a plurality of temporary retainingpins which are biased upwardly by an elastic member, and which lowerintegrally with the substrate holder against the elastic force of theelastic member as the substrate holder lowers, and return to theoriginal position as the substrate holder rises; wherein each of thetemporary retaining pins has a head portion having a tapered surfaceprovided so that, when placing the substrate on the temporary retainingpins, the tapered surface contacts a peripheral end surface of thesubstrate and effects positioning of the substrate, and having aretaining portion, projecting outwardly, for receiving thereon andretaining a peripheral lower surface of the substrate; and wherein thesubstrate holder having the substrate fixing ring, the seal ring, andthe temporary retaining section having the temporary retaining pins,which each have the retaining portion, are structured and arranged suchthat the substrate can be vertically moved with the retaining portionretaining the substrate by vertically moving the substrate holder andsuch that a gap is formed between the retaining portion and thesubstrate by holding the substrate by nipping a peripheral portion ofthe substrate between the substrate fixing ring and the seal ring. 2.The substrate processing unit according to claim 1, wherein thesubstrate processing unit is a pre-plating treatment unit for carryingout a pre-plating treatment of the substrate prior to plating.
 3. Thesubstrate processing unit according to claim 2, wherein the pre-platingtreatment unit is a catalyst-imparting treatment unit for imparting acatalyst to the surface of the substrate.
 4. The substrate processingunit according to claim 2, wherein the pre-plating treatment unit is acleaning treatment unit for cleaning the surface of the substrate.
 5. Asubstrate processing unit according to claim 1, wherein said retainingportion of said head portion projects outwardly of said tapered surfacein a horizontal direction.
 6. A substrate processing unit according toclaim 1, wherein said head portion has a flat top surface, with saidtapered surface extending from said flat top surface outwardly to saidretaining portion, and said retaining portion projecting outwardly, in ahorizontal direction, of said tapered surface.